Retention Effects Of The Materials Based On Rice-straw Biochar On Nitrogen And Phosphorus In The Soils From Rice-rapeseed Rotation System

The river system in Jianghan Plain is well developed.And the rice-rapeseed rotation is common.With highly intensive agriculture and extensive fertilizer management,the loss of nitrogen(N)and phosphorus(P)in paddy field is severe.Applying retention materials is an important measure of reducing the loss of N and P from rice-rapeseed rotation system.And it has great practical significance for improving water quality.In this study,we selected rice straw biochar(SB)and its mixed materials with fly ash(FA)or flue gas desulfurization gypsum as the experimental materials.To determine the retention effect of experimental materials on N and P in soil from the rice-rapeseed rotation systerm in Jianghan Plain,the soil column leaching experiment,rape pot experiment and paddy field experiment was conducted.Based on the changes of N and P in water,soil and plants,this paper studied the effect of experimental materials on leaching or retention of N and P from soil,explored the regulation effect of the materials on N and P retention during rape planting,and evaluated the field application effect of the materials on N and P retention during rice planting.The conclusions can provide new ideas for the reuse of waste resources,and reduce the loss of N and P from agricultural non-point source pollution.The main results of the paper are as follows:(1)In the soil column leaching experiment,different types and dosage of materials and different materials mixing ratio had different effects on N and P retention in soil.When the material was applied alone,the dosage of SB was 1% and3%,respectively,the retention effect on the N and P were the best.0.5% FA had good retention effects on N and P.When the materials were mixed,the mixed materials of SB and FA could better promote the retention of N and P.In addition,the retention effect of N increased with the increase of the proportion of SB,while that of P was better when the proportion of SB was low.(2)Under potted conditions,the retention effect of each material on N and P varied in different growth period of rape.In the seedling stage,the materials had good retention effects on N and P.When materials are the SB and FA in the proportion of1 :2 and 0.5% SB,respectively,the retention effect on the N and P were the best.The mixed material of SB and FGDG in the proportion of 1:1 had better N and P rentention effect.In the late seedling stage,the N and P rentention effect of each material was relatively weak.At flowering stage,the leaching loss of N decreased by less than 20 %,and all the materials increased the leaching loss of P.(3)In the field experiment,the mixed materials based on SB reduced the concentration of N and P in the surface water from paddy fields after fertilization,and reduced the risk of N and P loss.The single application of 0.2% SB was the most beneficial to N retention.The mixed application of SB and FGDG was more conducive to the retention of P.Moreover,each material had no adverse effect on rice yield and the uptake of N and P.(4)In soil column leaching experiment,rape pot experiment and paddy field experiment,due to the different amount of materials,soil scale effect and plant factors,the effects of various materials on soil nitrogen and phosphorus retention were different.Considering the effects of nitrogen and phosphorus retention,crop yield traits,material cost and operability,it was better to mix SB and FA with basal fertilizer,but the specific dosage and mixing ratio needed to be explored in long-term field trials.